PARASITISM IN MARINE ECOSYSTEMS THROUGH GEOLOGIC TIME

Temporal trends of parasite-host interactions and the ecological and evolutionary information they can provide are a burgeoning avenue of study. Biomineralized parasites, such as some platyceratid gastropods, may occasionally be found in association with the traces they produce/induce on their hosts. Soft-bodied parasites, such as trematodes and polychaetes, have a much lower preservation potential, but their presence may still be inferred from characteristic traces left on their hosts. Such traces and their interpretations are documented in the paleontological literature, and by synthesizing this data into a 'parasite database' it is possible to analyze trends as well as identify areas for future research. This presentation covers a portion of this ongoing parasite database; namely polychaete, trematode and gastropod parasitism in bivalves, crinoids and echinoids though geologic time.

Crinoids with parasitic traces date back to the Ordovician; traces on crinoid stems include swelling or gall-like structures, traces on crinoid calyxes include borings, and calyxes may also be found with gastropods attached. Gastropod borings may also be found in echinoids and date at least as far back as the Cretaceous. In bivalves, parasites may trigger a shell response to envelope the parasite; as such some traces may be gradational from trematode pits to the almost completely enveloped igloo structures. Other traces include U-shaped borings and mudblisters which are associated with polycheate infection, an internal shell ridge or Hohlkehle (lit. “hollow channel”), and internal septa. Pearl formation (blister-pearls, half-pearls, free-pearls) may also be the result of parasite infection, but without examining the nucleus of the pearl, inorganic origin or (at least in one case) infection with the larvae of another bivalve cannot be ruled out.

This parasite database, as it grows, could help test/direct investigation into whether there are any trends in prevalence and/or intensity in a taxonomic group over time, whether they correlate with trends in diversity, to what extent geography/environment affects parasite distribution/prevalence, and if there are any trends in host-selectivity over time; thereby improving understanding of parasite-host interaction at a global and temporal scale.